CN111893418A - A method for improving the high temperature oxidation resistance of nickel-based alloy surfaces - Google Patents

Abstract

The invention discloses a method for improving the high temperature oxidation resistance of a nickel-based alloy surface. The force analysis of a multi-layer coating powder model is carried out to obtain a coating powder proportion model, and how to select the powder shape and proportion is disclosed; Next, the thermal spraying process is used to preset the proportioned coating powder on the surface of the pretreated substrate; finally, the substrate preset coating is modified by electron beam cladding to make the powder coating The full-melting matrix is micro-melted, and the elements in the fusion zone diffuse each other to obtain a metallurgical bonding coating. The present invention selects powder with a suitable particle size to prepare a high-temperature protective coating, which can improve the high-temperature oxidation resistance of the matrix.

Description

A method for improving the high temperature oxidation resistance of nickel-based alloy surfaces

technical field

The invention relates to the technical field of surface modification protection, in particular to a method for improving the high temperature oxidation resistance of a nickel-based alloy surface.

Background technique

Inconel718 alloy is a precipitation-strengthened nickel-based superalloy. It is the most widely used nickel-based superalloy and one of the most critical superalloys in the aviation industry at this stage. It is widely used in aero-engine turbine disks, fasteners and blades, etc. At the hot end, the service environment is extremely harsh. This hot end part is required to withstand high temperature oxidation and high temperature corrosion, and the use environment is extremely harsh, often accompanied by high speed, high temperature and thermal stress, but at present, the material has relatively weak resistance to high temperature oxidation.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for improving the high-temperature oxidation resistance of the surface of the nickel-based alloy, and to improve the high-temperature oxidation resistance of the surface of the nickel-based alloy.

In order to achieve the above object, the present invention provides a method for improving the high temperature oxidation resistance of the nickel-based alloy surface, comprising:

The force analysis of the multi-layer coating powder model was carried out, and the coating powder ratio model was obtained;

The thermal spraying process is used to preset the proportioned coating powder on the pretreated substrate surface;

The substrate pre-coating is modified by electron beam cladding to obtain a metallurgical bonding coating.

Among them, the force analysis of the multi-layer coating powder model is carried out, and the coating powder ratio model is obtained, including:

Perform force analysis on the first layer and second layer of coating powder in the obtained multi-layer uniform coating powder model, and combine the corresponding electron beam force, when the obtained horizontal thrust and resistance are equal, the coating is obtained. Powder proportioning model.

Wherein, the thermal spraying process is used to pre-set the coating powder that has been proportioned on the surface of the pretreated substrate, including:

The pretreated substrate is preheated with a flame flow temperature of 100°C to 200°C, and the coating powder whose powder ratio is completed according to the coating powder ratio model is heated to a molten or semi-molten state. Spray onto the pretreated surface of the substrate.

Wherein, the substrate preset coating is modified by electron beam cladding to obtain a metallurgical bonding coating, including:

Under the high-voltage electric field, the emitted electrons are collected into electron beams by the condenser, and bombarded on the pre-coated substrate at a distance of 120-300mm from the electron gun. At the same time, the energy conversion of the electron beam is used to convert the The coating is completely melted, and the specified part of the substrate is melted at the same time to obtain a metallurgically bonded coating.

Wherein, the method also includes:

The parameters of the cladding process are the vacuum degree of the welding chamber 3.5×10 ^-2 Pa, the vacuum degree of the gun chamber 4.4 x 10 ^-3 Pa, the scanning power is 0~9kW, the accelerating voltage is 0~60kV, the scanning beam current is 40~80mA, the focusing The current is 300～380mA, the scanning speed is 400～800mm/min, the scanning shape is circular, and the frequency is 600f/H _Z .

In the method for improving the high temperature oxidation resistance of the nickel-based alloy surface of the present invention, the force analysis of the multi-layer coating powder model is carried out to obtain the coating powder proportion model, and how to select the powder shape and proportion is disclosed; , using the thermal spraying process to preset the proportioned coating powder on the pretreated substrate surface; finally, use electron beam cladding to modify the substrate preset coating to make the powder coating fully The melted matrix is micro-melted, and the elements in the fusion zone diffuse each other to obtain a metallurgical bonding coating. The present invention selects powder with a suitable particle size to prepare a high-temperature protective coating, which can improve the high-temperature oxidation resistance of the matrix.

Description of drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained according to these drawings without creative efforts.

1 is a schematic diagram of steps of a method for improving the high temperature oxidation resistance of a nickel-based alloy surface provided by the present invention.

Fig. 2 is the force model of the coating powder provided by the present invention.

FIG. 3 is a force analysis diagram provided by the present invention.

Detailed ways

The following describes in detail the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary, and are intended to explain the present invention and should not be construed as limiting the present invention.

In the description of the present invention, "plurality" means two or more, unless otherwise expressly and specifically defined.

Referring to FIG. 1, the present invention provides a method for improving the high temperature oxidation resistance of a nickel-based alloy surface, comprising:

S101 , cleaning and pre-processing the obtained substrate.

Specifically, in order to improve the oxidation resistance of Inconel718, the substrate surface of 50×30×10mm was first ground and polished with 660# sandpaper to remove the oxide skin; 800# sand was used to continue grinding and polishing the substrate to roughen the surface. Increase the surface area and unevenness, and improve the bonding force; then wipe with an alcohol-containing cotton ball, and finally wipe the surface of the substrate with a cotton ball dipped in acetone solution and dry it to ensure removal of grease and rust on the surface of the substrate. The mechanical bond strength of the matrix.

S102, performing force analysis on the multi-layer coating powder model to obtain a coating powder ratio model.

Specifically, it is assumed that the coating powders are spherical powders with equal diameters, and are preset on the surface of the substrate in a multi-layered and uniform manner. of the accelerating voltage. Assuming that an electron moves at a velocity V under the action of an accelerating voltage U, the kinetic energy obtained by the electron is:

You can get:

When the electrons enter the high-voltage electric field between the cathode and anode, they obtain a constant acceleration under the action of the electric field force, and the speed increases continuously in the process of moving to the anode, thus obtaining a high kinetic energy. The electron beam coming out of the electric field is focused under the action of the electromagnetic lens, which obtains a practical electron beam current with extremely high energy density. When the electron beam with high energy density acts vertically on the surface, according to the momentum theorem, unit time The electron beam force F can be expressed as:

Wherein, I ₀ is the electron beam current; me = 9.11×10 ^-31 Kg is the electron mass; U is the accelerating voltage; _e =1.6×10 -19 C is the electron quantity.

The first layer of powder is subjected to a vertical downward force, as shown in Figure 3(a), and the second layer of powder will generate a horizontal thrust under the vertical pressure of the first layer of powder, as shown in Figure 3(b).

Assume that the electron beam force on each powder in the above model is:

Then the horizontal thrust on the powder is:

The resistance to the powder is:

Where; d is the diameter of the powder, d ₀ is the diameter of the electron beam spot, and d ₀ >d; G is the gravity of each powder, and μ is the friction coefficient between the powders.

When F ₂ =F _p , the maximum processing current can be obtained, that is, the coating powder ratio model:

Among them: ρ is powder density; g is gravitational acceleration.

It is not difficult to find that if the powder particle size is too large, the thickness of the preset coating will be increased. If the coating is too thick, the penetration force of the electron beam has a certain limit, and a better metallurgical bonding layer cannot be completed, thus affecting the quality of the cladding layer. . Therefore, it is necessary to experiment with presets by mixing thickness and shape, so that the purpose of mixing is to increase the mechanical bite force between the powders.

S103 , adopting a thermal spraying process, and presetting the proportioned coating powder on the surface of the pretreated substrate.

Specifically, the pretreated substrate is preheated by controlling the temperature of the flame flow of the spray gun at 100-200°C. It should be noted that the flame flow should not be too close to the surface of the workpiece to avoid the phenomenon of sudden heating on the surface of the workpiece, and there should be no heating effect. Uniform phenomenon, different spraying parts, the preheating temperature and preheating method should also be different. The purpose of preheating is to eliminate the moisture on the surface of the workpiece, increase the temperature of the interface between the coating and the substrate during spraying, and reduce the substrate and coating materials. The residual stress caused by the difference in expansion can avoid the resulting cracking of the coating and improve the bonding strength of the coating and the substrate. Then spray the coating powder with a diameter ranging from 35-50nm on the base sample and complete the powder proportioning according to the coating powder proportioning model, and heat the sprayed material to a molten or semi-molten state. It is atomized and accelerated so that it is sprayed onto the surface of the workpiece at a high speed to form a coating with special properties, and the thickness of the spray is 1mm.

In order to improve the performance and service life of the substrate, the surface protection of the coating is selected. As a high temperature resistant protective coating, MCrAlY is widely used in hot end components such as aero-engine blades in R&D and production, and the choice is more flexible. Different alloy compositions are designed according to different environments. Finally, the NiCoCrAlY powder that can protect the high-temperature base alloy from being oxidized and is an anti-oxidation alloy is selected. Ni, Co, and Cr are the main elements of the coating. The chemical composition content is shown in Table 1. Al and Y are trace elements. The anti-oxidation mechanism is to form a dense Al ₂ O ₃ oxide film on the surface in a high temperature environment, and the presence of Cr can also promote the formation of Al ₂ O ₃ , and the formation of Cr ₂ O ₃ prevents further oxidation. The role of rare earth element Y is Absorbs oxygen in the alloy and improves the adhesion strength of the oxide film to the metal substrate.

Table 1 Chemical composition content of coating NiCoCrAlY powder (wt%)

element Ni Co Cr Al Y wt margin 22.0～24.0 19.0～21.0 7.5～8.5 0.4～0.8

The thermal spray coating and the substrate are mechanically combined, and the bonding strength is low, only equivalent to 5 to 30% of the substrate material. Sometimes the coating peels off. When cooling, the shrinkage of the coating and the substrate is inconsistent, and tensile stress is generated in the coating. When the bonding strength is lower than the tensile stress of the coating, the peeling phenomenon occurs. When the tensile stress in the coating is less than the bonding strength of the film base but greater than the tensile strength of the coating, the coating will crack. Therefore, when spraying, you must choose a suitable thickness, generally ranging from a few microns to a few millimeters, and choose a suitable preheating temperature to preheat, and then slowly cool.

In the present invention, NiCoCrAlY powder is pre-positioned on the substrate by thermal spraying process. The process is simple, the coating thickness is controllable, the deposition efficiency is high, the production cost is low, and it can be prepared in a large area, which further broadens the application field of nickel-based alloys. Surface modification. The cost of raw materials and processing can be saved, and the cheap base material can be more widely used. However, there are certain pores in the sprayed coating, which is unfavorable for environments that require chemical resistance. Therefore, the present invention continues to perform cladding treatment on the sprayed coating by electron beam, so as to reduce the porosity defect of the coating, and make the mechanical combination of the coating and the substrate become a metallurgical combination.

S104, using electron beam cladding to modify the substrate preset coating to obtain a metallurgical bonding coating.

Specifically, it is considered that the thermal spray coating pre-installed on the surface of the substrate is not high in bonding strength, and has shortcomings such as pores. Therefore, high-energy density electron beams are used for cladding. During electron beam cladding, the cathode of the electron gun emits electrons, which are converged into electron beams by the condenser, and are accelerated in a directional manner under the action of a high-voltage electric field. At this time, the speed of electrons is adjusted to, close to, or reach half the speed of light, and has high kinetic energy. The electron beam is concentrated into a finer beam through the action of the focusing coil and the deflection coil. When the electron beam bombards the surface of the material, the kinetic energy of the electron beam is converted into heat energy, and the high-energy density electron beam heat source instantly deposits the energy on the surface of the coating, so that the material can be rapidly heated to above the phase transition temperature or melting temperature, which can make the coating completely Melting, the substrate is partially melted, thereby increasing the bonding strength between the coating and the substrate, but instead of using the molten metal on the surface of the substrate as a solvent, the separately configured alloy powder is melted to become the main alloy of the cladding layer. The base alloy also has a thin layer that melts, forming a metallurgical bond with it, which greatly improves the coating properties.

The obtained sprayed sample is placed in an electron beam vacuum processing equipment for cladding, and the cladding sample is 120-300 mm away from the electron gun. The parameters of the cladding process are as follows: the vacuum degree of the welding chamber is 3.5×10 ^-2 Pa, the vacuum degree of the gun chamber is 4.4×10 ^-3 Pa, the scanning power is 0~9kW, the accelerating voltage is 0~60kV, the scanning beam current is 40~80mA, The focusing current is 300-380 mA, the scanning speed is 400-800 mm/min, the scanning shape is circular, and the frequency is 600 f/H _Z .

Different process parameters can be selected for cladding:

The first surface is uneven, and there are small balls around it, and the second surface is uneven, and there are large balls in the middle. The third pass is relatively good as a whole, indicating that the pre-coating of the sample melts rapidly under this process parameter, and a uniform molten pool is formed in a very short time. The surface coating of the melting channel quickly re-solidifies after scanning, resulting in a flat and metallic surface, and the surface is smooth without defects such as cracks and pores, and has obvious metallic luster. The surface quality of the cladding layer is very ideal, and there is no appearance. bad. The morphology of the cladding layer is closely related to the incident energy of the electron beam and the molten pool. When the electron beam current is small, the cladding layer powder does not melt, but the excessive beam current will cause the cladding layer to be rough; Fish-scale grooves are formed on the surface of the morphology, which has a great relationship with the fluidity of the molten pool; different beam spot diameters can easily cause heat concentration and over-melting phenomenon. Therefore, the optimum process parameters for this electron beam cladding NiCoCrAlY coating are: electron beam current of 20mA, beam spot diameter of 5mm, scanning speed of 8mms ^-1 , acceleration voltage of 60Kv, and preset powder thickness of 1mm.

In the invention, a NiCoCrAlY coating is prepared on the surface of an Inconel718 alloy substrate by a combined process of thermal spraying and electron beam cladding, so as to improve the high-temperature oxidation resistance of the surface of the nickel-based alloy. It mainly discloses how to select the powder shape and proportion, and the specific steps and parameter settings for preparing the high temperature oxidation resistant coating on the surface of the substrate by using the combined process of thermal spraying and electron beam cladding. From the study of the force of the electron beam on the powder pre-installed on the substrate, the influence of the particle size and shape of the powder on the quality of the cladding layer is deduced in detail; the mechanical bite force between the powders is increased by the combination of thickness and shape and the experimental It is found that the coating quality is the best when the thickness ratio is 3:2. In addition, preheating, pre-sintering, and accompanying heat treatment are used to increase the mechanical bonding strength of the substrate surface during the thermal spraying preset; the electron beam processing time is fast, the action time is short, and the coupling between the end surface and the vacuum environment is good. During the electron beam cladding process, the thermally sprayed coating and the substrate form a metallurgical bond in the cladding area, and reduce defects such as pores. The high temperature oxidation resistant coating prepared by this method improves the use range of nickel-based alloys in harsh environments, and at the same time, the preparation process described in the present invention is simple, the coating thickness is controllable, the production cost is low, and it can be used in a large area. It is suitable for industrial production, and greatly promotes the application of nickel-based alloys at high temperatures.

In the method for improving the high temperature oxidation resistance of the nickel-based alloy surface of the present invention, the force analysis of the multi-layer coating powder model is carried out to obtain the coating powder proportion model, and how to select the powder shape and proportion is disclosed; , using the thermal spraying process to preset the proportioned coating powder on the pretreated substrate surface; finally, use electron beam cladding to modify the substrate preset coating to make the powder coating fully The melted matrix is micro-melted, and the elements in the fusion zone diffuse each other to obtain a metallurgical bonding coating. The present invention selects powder with a suitable particle size to prepare a high-temperature protective coating, which can improve the high-temperature oxidation resistance of the matrix.

The above disclosure is only a preferred embodiment of the present invention, and of course, it cannot limit the scope of rights of the present invention. Those of ordinary skill in the art can understand that all or part of the process of implementing the above embodiment can be realized according to the rights of the present invention. The equivalent changes required to be made still belong to the scope covered by the invention.

Claims (5)

1. A method for improving the high temperature oxidation resistance of the surface of a nickel-based alloy is characterized by comprising the following steps:

carrying out stress analysis on the multilayer coating powder model to obtain a coating powder proportioning model;

presetting the coating powder which is matched to the surface of the pretreated substrate by adopting a thermal spraying process;

and modifying the matrix preset coating by using electron beam cladding to obtain the metallurgical bonding coating.

2. The method for improving the high temperature oxidation resistance of the surface of the nickel-based alloy according to claim 1, wherein the stress analysis is performed on the multilayer coating powder model to obtain a coating powder proportioning model, and the method comprises the following steps:

and (3) carrying out stress analysis on the first layer and the second layer of coating powder in the obtained multilayer uniform coating powder model, and combining corresponding electron beam acting force to enable the obtained horizontal thrust and resistance to be equal, so as to obtain a coating powder proportioning model.

3. The method for improving the high temperature oxidation resistance of the surface of the nickel-based alloy according to claim 2, wherein the pre-preparing the coating powder with the finished proportioning to the surface of the pretreated substrate by adopting a thermal spraying process comprises the following steps:

preheating the pretreated substrate by using the flame flow temperature of 100-200 ℃, heating the coating powder which completes powder proportioning according to the coating powder proportioning model to a molten or semi-molten state, and simultaneously spraying the coating powder to the surface of the pretreated substrate.

4. The method for improving the high temperature oxidation resistance of the surface of the nickel-based alloy according to claim 3, wherein the modifying the base pre-coating layer by electron beam cladding to obtain the metallurgical bonding coating comprises:

under a high-voltage electric field, converging the emitted electrons into an electron beam by using a beam converging electrode, bombarding the electron beam onto the substrate which is 120-300 mm away from an electron gun and is provided with a coating, simultaneously, completely melting the coating by using energy conversion of the electron beam, and simultaneously melting the appointed part of the substrate to obtain the metallurgical bonding coating.

5. The method for improving the high temperature oxidation resistance of a surface of a nickel-base alloy of claim 4, further comprising:

the parameter range of the cladding process is that the vacuum degree of a welding chamber is 3.5 multiplied by 10^-2Pa, gun chamber vacuum degree 4.4X 10^-3Pa, scanning power of 0-9 kW, accelerating voltage of 0-60 kV, scanning beam current of 40-80 mA, focusing current of 300-380 mA, scanning speed of 400-800 mm/min, circular scanning shape and frequency of 600f/H_Z。

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